After a delta-sigma modulator emerges, recently it is prevailing due to the rapid progress of semi-conductor technology. The most of IC manufacturers produce these products and apply them in the communication, multimedia, signal processing and so on for converting signals to digital or analog.
A prior second-order delta-sigma modulator can process a signal via two integrators (operational amplifiers) and a quantizer (comparator), and feed the signal back to an input terminal of the integrator. FIG. 1 illustrates a prior delta-sigma modulator. As shown in FIG. 1, a delta-sigma modulator 1 transmits an signal operated by a first adder orderly to a first integrator 110, a second adder 101, a second integrator 111 and a quantizer 112, and converts the signal to a digital signal via quantizer 112. Finally, the digital signal is processed by a digital-to-analog converter and then fed back to the first adder and the second adder in order to operate the signal with addition or subtraction in the adders.
The circuit of the delta-sigma modulator 1 can estimate a signal roughly, measure a delta and compensate the delta with integration. If the integration of the delta is finite, the average value of the final output signal equals average value of the input signal. The same principle also applies to multi-order delta-sigma modulator, and the output is log2N bits when the order is N. Besides, the higher the order, the better the noise shaping. Usually, the second-order delta-sigma modulator circuit is the one-bit status and it is to say that the output is only “1” or “0.” Hence, all the range of voltage is linear, and that's why the delta-sigma modulator can perform a high accuracy.
With the development of nanotechnology, the demand for the electronic components with tiny size and energy saving becomes more and more increasing, and the modulator is no exception. However, the original modulator comprising integrators composed of operational amplifiers can not meet the demand nowadays. Therefore, it brooks no delay to invent a modulator with less power consumption and higher efficiency. In order to overcome the drawbacks of the prior modulator, the inventors research and experiment without giving up, and finally invent “Fully Differential Delta Sigma Modulator” to overcome the drawbacks. The summary of the present invention is described as follows.